1. Field of the Invention
The present invention relates to a switch module which selectively connects a plurality of antenna elements and a plurality of communication systems.
2. Description of the Related Art
In recent years, as a mobile communication terminal such as a cellular phone or a mobile information terminal or a communication apparatus such as a wireless LAN terminal, a communication apparatus has been provided and includes a plurality of communication systems performing communications according to different communication standards such as the GSM (Global System for Mobile communications: registered trademark) standard, the W-CDMA (Wideband Code Division Multiple Access) standard, the LTE (Long Term Evolution) standard, and the Bluetooth (registered trademark) standard; and supports communications according to a plurality of communication standards (multi-modes). In addition, in a communication apparatus which supports multi-modes by including a plurality of communication systems, a predetermined frequency band is assigned to each communication system, and communication is performed by using a plurality of frequency bands (multi-bands). Moreover, as a communication apparatus which supports multi-modes as described above, a communication apparatus has also been provided which includes a communication system for receiving a signal from a GPS (Global Positioning System) satellite, in addition to the respective communication systems which perform communication according to the above respective communication standards.
As an existing communication apparatus which supports multi-modes and multi-bands as described above, a communication apparatus has been provided which includes a first communication system performing wireless communication via a wireless LAN using a 5 GHz band standardized as IEEE802.11a; and a second communication system performing wireless communication via a wireless LAN using a 2.4 GHz band standardized as IEEE802.11b (e.g., see Japanese Unexamined Patent Application Publication No. 2010-252346 (paragraphs [0033] to [0053], FIGS. 1 to 3, etc.)). As shown in FIG. 13, a communication apparatus 500 disclosed in Japanese Unexamined Patent Application Publication No. 2010-252346 includes two multi-band antennas 501a and 501b which are able to perform transmission/reception in the 2.4 GHz band and the 5 GHz band; an RF-IC 502 in which a transmitting circuit section which modulates transmission data and a receiving circuit section which demodulates reception data are provided for each communication system; and a switch module 503 (high frequency circuit section) which selectively connects the respective multi-band antennas 501a and 501b and the transmitting circuit section and the receiving circuit section for each communication system provided in the RF-IC 502. In addition, baluns 504a and 504b which convert a balanced signal outputted from each transmitting circuit section into an unbalanced signal are provided between the switch module 503 and the transmitting circuit section for each communication system provided in the RF-IC 502, and power amplifiers 505a and 505b which amplify the unbalanced signal and output the unbalanced signal to the switch module 503 are provided so as to be connected to the subsequent stages of the respective baluns 504a and 504b. 
In addition, the switch module 503 is formed of switching elements such as a field effect transistor (FET) and a diode, and includes a DPDT (Double Pole Double Throw) high-frequency switch circuit having first to fourth ports, and a plurality of branching circuits. The multi-band antennas 501a and 501b connected to the first and second ports 503a and 503b, respectively, of the high-frequency switch circuit and the branching circuits connected to the third and fourth ports, respectively, of the high-frequency switch circuit are selectively connected to each other by the high-frequency switch circuit, whereby the multi-band antennas 501a and 501b and the transmitting circuit section and the receiving circuit section for each communication system which are provided in the RF-IC 502 and connected to the respective branching circuits are selectively connected to each other by the switch module 503.
Moreover, in the communication apparatus 500, communication by diversity is executed by using the multi-band antennas 501a and 501b. Specifically, first, before the communication is started, the multi-band antenna 501b and both communication systems are connected to each other by the switch module 503, and frequency scan is performed to search for a frequency channel on which reception is possible (carrier scan), whereby all frequency channels on which reception is possible are detected. Next, the other multi-band antenna 501a and both communication systems are connected to each other via the switch module 503, and frequency scan is performed to search for a frequency channel on which reception is possible, whereby all frequency channels on which reception is possible are detected. Subsequently, a frequency channel for a communication system to be activated is selected on the basis of a result of the frequency scan using both multi-band antennas 501a and 501b. In addition, the signal levels (amplitudes) of reception signals received by both multi-band antennas 501a and 501b are compared to each other, whereby a multi-band antenna to be connected to the transmitting and receiving circuits of the selected communication system is selected from the multi-band antennas 501a and 501b. Then, the selected multi-band antenna and the selected communication system are connected to each other by the switch module 503, and communication using the multi-band antenna and the communication system is executed in the communication apparatus 500.
Meanwhile, in the above-described switch module 503, the multi-band antennas 501a and 501b (antenna elements) are connected to the first and second ports 503a and 503b of the high-frequency switch circuit via matching circuits (not shown), respectively, and impedance is matched between each of the multi-band antennas 501a and 501b and the switch module 503, whereby the insertion loss of the switch module 503 is reduced. However, in this case, since it is necessary to provide the matching circuits for the respective multi-band antennas 501a and 501b connected to the switch module 503, the manufacturing cost of the communication apparatus 500 is increased. Therefore, there is a demand for a switch module which has low insertion loss and does not need a matching circuit between each connected antenna element.
In addition, the above-described switch module 503 is formed such that, in order to reduce transmission loss of a communication signal due to switch units being connected at multiple stages, the number of switch units is reduced and a plurality of branching circuits are connected to one switch unit (high-frequency switch circuit). However, with an increase in the number of communication systems mounted in the communication apparatus 500, the number of branching circuits connected to the switch unit has to be increased, and the number of terminals of the switch unit connected to each branching circuit has to be increased. In this case, with the increase in the number of the terminals of the switch unit and the increase in the number of the branching circuits connected thereto, the insertion loss of the switch module may increase. However, such an increase in the insertion loss of the switch module with an increase in the number of the supported communication standards (modes) has not been sufficiently considered. Therefore, there is a demand for a switch module which is able to reduce insertion loss even when the number of modes supported by the switch module increases and the number of frequency bands (bands) used for communication increases.